1. Field of the Invention
The present invention relates to an information storage apparatus and methods of writing, reading and erasing information using the same, and more particularly, to a high-density information storage apparatus using electron emission and methods of writing, reading and erasing information using the same.
2. Description of the Related Art
Recently, as recording media enabling high-density recording are developed, devices using them have been developed. Information storage apparatuses with a high-density information recording medium such as CDs or DVDs write information to the high-density recording medium, or read or erase information from the high-density recording medium using a laser. Accordingly, it is preferable to use a short-wavelength laser beam which can reduce the area of a beam spot formed on the surface of a high-density recording medium in order to write information to the high-density recording medium.
Since there is a limit in decreasing the wavelength of a laser beam, the performance of information storage apparatuses for writing, reading and erasing information using a laser beam is also limited.
Meanwhile, vertical magnetic recording apparatuses which use a probe instead of a laser for writing, reading and erasing information have limited storage performance depending on the size of the probe.
Therefore, there have been provided alternative methods of bringing a tip, which is used for a scanning probe microscope (SPM) or an atomic force microscope (AFM), in contact with or close to a recording medium to write, read or erase information. The AFM falls under the SPM and uses atomic force between a tip and a sample. However, such methods have problems with abrasion and vibration of a tip and slow recording and writing speed.
FIG. 1 is a schematic diagram of a disc apparatus using a conventional SPM probe. Referring to FIG. 1, the disc apparatus includes a disc 8, a head 9, and an optical system 100. The disc 8 includes a circular substrate 8a, an electrode layer 8b formed on the circular substrate 8a, and a ferroelectric layer 8c formed on the electrode layer. The head 9 includes a microtip 9a for writing information by polarizing the ferroelectric layer 8c and for plying the surface of the disc 8 by an amount corresponding to a quarter of the wavelength of light in a vertical direction from the surface of the disc 8 according to the polarity of the dielectric polarization to read information, and a reflective unit for reflecting light. The optical system 100 recognizes a difference in optical path attendant on the vertical reciprocating motion of the head 9 to detect the recording information.
For the disc 8, the electrode layer 8b and the ferroelectric layer 8c, to which information is written using dielectric polarization, are sequentially stacked on the circular substrate 8a. The head 9 is realized as an SPM probe. The head 9 includes a microtip 9a, a reflector 9b for reflecting light, and an arm 9c for supporting the microtip 9a and the reflector 9b. The optical system 100 includes a laser diode, i.e., a light source 1, a collimating lens 2 for converting light emitted from the light source 1 into a parallel beam, a beam splitter 3 for transmitting light and reflecting light reflected from the disc 8, an objective lens 5 for focusing light onto a track of the disc 8 to a diffraction limit, a focusing lens 4 for focusing the reflected light, and a photodetector 7 for converting the focused reflected light into an electrical signal.
The disc apparatus operates according to the following principle. When a slight portion of a ferroelectric film deposited on an electrode plate is polarized using a microtip electrode, the polarized portion can be discriminated from an unpolarized or reverse polarized portion by moving the microtip 9a to which a predetermined voltage is applied and understanding a difference in electrostatic force therebetween. Accordingly, a different magnitude of electrostatic force is applied to the microtip 9a of the head 9, to which the predetermined voltage is applied, according to the degree of polarization on the surface of the disc 8. The electrostatic force raises or drops the microtip 9a by xcex/4. Only light having an optical path difference of xcex/2 is split by the beam splitter 3 to be incident to the photodetector 7 and then detected by the photodetector 7.
As described above, in the SPM technique of measuring phenomena acting between a probe and a sample using physical instruments and laser beams, it is required that the tip of the probe be extremely close to the sample, and the tip be very sharp. Accordingly, the tip is easily worn away. When the tip is worn away or vibrates, the distance between the tip point and the sample changes, which makes it difficult to precisely write or read information. In addition, a high degree of dependence on the flatness of a recording medium results in relatively low information writing or reading speed.
To solve the above-described problems, it is a first object of the present invention to provide an information storage apparatus for overcoming a problem of abrasion or vibration of a member such as a tip used for writing and reading information, preventing information writing and reading speed from dropping, and storing much more information in a unit area.
It is a second object of the present invention to provide methods of writing, reading and erasing information using the above information storage apparatus.
To achieve the first object of the invention, there is provided a high-density information storage apparatus including a lower electrode, a photoconductive layer and a recording medium sequentially provided on the lower electrode, a conductive layer converting unit for making the photoconductive layer conductive, a data write and read unit for writing data to the recording medium or reading data from the recording medium, a data loss preventing unit for preventing loss of data during data write and read operations, and a power supply connected to the lower electrode and the data write and read unit, for supplying voltage necessary for reading and writing data.
Here, the recording medium is a material layer in which the conductivity changes when charged particles are injected thereto and is realized as an amorphous dielectric substrate. The data write and read unit is a charged particle emitting unit which writes data by injecting charged particles into the recording medium and reads data by detecting charged particles emitted from the recording medium.
The high-density information storage apparatus further includes a gate between the charged particle emitting unit and the recording medium. The gate allows only some of the charged particles emitted from the charged particle emitting unit (the recording medium) to reach the recording medium (the charged particle emitting unit).
The power supply includes a first power supply for applying a predetermined voltage between the lower electrode and the gate, and a second power supply for applying a predetermined voltage between the gate and the charged particle emitting unit.
The charged particle emitting unit includes an emitter for emitting charged particles, and an emitter holder connected to the power supply and disposed above the recording medium, for controlling the motion of the emitter.
In addition, the data loss preventing unit is a charged particle control unit for controlling charged particles emitted from the emitter so that they reach a predetermined region of the recording medium directly below the emitter or controlling charged particles emitted from the recording medium so that they reach the emitter directly above the recording medium. The data loss preventing unit is realized as a magnet. Here, the magnet includes a first magnet provided above the emitter holder and a second magnet provided below the lower electrode. The first and second magnets may be realized as a single permanent magnet or as separated permanent magnets. The first and second magnets may be realized as a single electromagnet or as separated electromagnets that have opposite poles facing each other. The magnet may be an electromagnet surrounding at least the charged particle emitting unit and the recording medium.
The conductive layer converting unit is a light source radiating light onto the photoconductive layer and is provided proximal to and above the recording medium, provided at the emitter holder and surrounding the emitter, or provided at the emitter holder but separated from the emitter.
The high-density information storage apparatus further includes a second photoconductive layer and a second recording medium onto which the conductive layer converting unit radiates light, the second photoconductive layer and the second recording medium being sequentially provided on the lower surface of the lower electrode; and a second data write and read unit provided below the second recording medium. Here, the second data read and write unit is a second charged particle emitting unit having the same function as the data read and write unit with respect to the second recording medium. The second charged particle emitting unit is configured in the same manner as the charged particle emitting unit.
The data loss preventing unit is a charged particle control unit for controlling charged particles emitted from the emitter so that they reach a predetermined region of the recording medium directly below the emitter or controlling charged particles emitted from the recording medium so that they reach the emitter directly above the recording medium, and for controlling charged particles emitted from the second emitter so that they reach a predetermined region of the second recording medium directly below the second emitter or controlling charged particles emitted from the second recording medium so that they reach the second emitter directly above the second recording medium. Here, the charged particle control unit is realized as a permanent magnet or electromagnet.
The conductive layer converting unit is a light source radiating light onto the photoconductive layer and the second photoconductive layer. The conductive layer converting unit includes a first light source provided proximal to and above the charged particle emitting unit and a second light source provided proximal to and below the second charged particle emitting unit, a first light source provided at the emitter holder and surrounding the emitter and a second light source provided at the second emitter holder and surrounding the second emitter, or a first light source provided at the emitter holder but separated from the emitter and a second light source provided at the second emitter holder but separated from the second emitter.
The lower electrode includes a first lower electrode contacting the photoconductive layer and a second lower electrode contacting the second photoconductive layer and insulated from the first lower electrode. Here, the conductive layer converting unit is a light source radiating light onto the photoconductive layer and the second photoconductive layer and is provided between the first and second lower electrodes in the shape of a plate.
The light source in the shape of a plate provided between the first and second lower electrodes includes a first plate light source radiating light onto the photoconductive layer and a second plate light source radiating light onto the second photoconductive layer.
The lower electrode includes a first lower electrode contacting the photoconductive layer and a second lower electrode contacting the second photoconductive layer and insulated from the first lower electrode, and the magnet includes a first magnet provided above the emitter holder, a second magnet provided below the second emitter holder, and a third magnet provided between the first and second lower electrodes. Here, the conductive layer converting unit radiates light onto the photoconductive layer and the second photoconductive layer. The conductive layer converting unit includes a first light source provided proximal to and above the charged particle emitting unit and a second light source provided proximal to and below the second charged particle emitting unit, a first light source provided at the emitter holder and surrounding the emitter and a second light source provided at the second emitter holder and surrounding the second emitter, a first light source provided at the emitter holder but separated from the emitter and a second light source provided at the second emitter holder but separated from the second emitter, or a first light source provided between the first lower electrode and the third magnet, for radiating light onto the photoconductive layer, and a second light source provided between the second lower electrode and the third magnet, for radiating light onto the second photoconductive layer.
To achieve the second object of the invention, there is provided an information writing method using the above high-density information storage apparatus. The information writing method includes a first step of adjusting the distance between the recording medium and a charged particle emitting area of the charged particle emitting unit, and a second step of injecting charged particles into the recording medium, thereby forming a conductive region corresponding to predetermined data in the recording medium.
It is preferable that the charged particles are injected under the influence of a magnetic field to prevent the charged particles from being lost while the charged particles emitted from the charged particle emitting area is travelling to a predetermined region of the recording medium directly below the charged particle emitting area. Here, the magnetic field is induced using a first magnet provided above the charged particle emitting unit and a second magnet provided below the lower electrode or using an electromagnet surrounding at least the recording medium and the charged particle emitting area.
The intensity of the magnetic field is adjusted by adjusting current flow through the electromagnet so that the charged particles emitted from the charged particle emitting area can reach the predetermined region of the recording medium directly below the charged particle emitting area even when the initial distance between the recording medium and the charged particle emitting area changes.
To achieve the second object of the invention, there is provided an information reading method using the above high-density information storage, apparatus. The information writing method includes a first step of adjusting the distance between the recording medium and a charged particle emitting area of the charged particle emitting unit, and a second step of reading data from the recording medium by recognizing charged particles emitted from the recording medium while moving the charged particle emitting area above the recording medium.
The charged particles are emitted from the recording medium under the influence of a magnetic field having a predetermined intensity so that the charged particles are not lost until they reach the charged particle emitting area disposed directly above. Here, it is preferable that the magnetic field is the same as that in the information writing method.
The intensity of the magnetic field is adjusted by adjusting current flow through the electromagnet so that the charged particles emitted from the recording medium can reach the charged particle emitting area of the charged particle emitting unit directly above the recording medium even when the distance between the recording medium and the charged particle emitting area changes.
To achieve the second object of the invention, there is provided an information erasing method using the above high-density information storage apparatus. In one embodiment, the information erasing method includes a first step of grounding the lower electrode, and a second step of discharging charged particles injected into the recording medium through lower electrode by converting the photoconductive layer into a conductive layer, thereby erasing data from the recording medium.
The second step discharges the charged particles injected into a predetermined region of the recording medium contacting the photoconductive layer through the lower electrode by selectively converting a predetermined region of the photoconductive layer into a conductive layer, thereby selectively and partially erasing data from the recording medium.
In another embodiment, the information erasing method includes a first step of grounding the lower electrode, and a second step of discharging all charged particles injected into the recording medium through lower electrode by converting the entire photoconductive layer into a conductive layer, thereby entirely erasing all data from the recording medium.
By using such a high-density information storage apparatus according to the present invention, a conventional problem of a damaged tip is avoided, and information processing speed during write, read and erasing operations is increased. In addition, since charged particles such as electrons are used for information processing, the information storage density of a recording medium can be increased compared to a conventional apparatus using a laser or probe.